Field of the Invention
The present invention relates to a machine tool, and more particularly, to a machine tool with a thermal displacement correction function.
Description of the Related Art
Previously, there have been used numerical control machine tools each of which includes: a main shaft fixed to a straight line movement shaft; a table having two or more straight line movement shafts; a rotating table with a rotating shaft, which is provided on the table and fixes a machining work; and a numeric value control device for controlling the main shaft and the tables. In the numerical control machine tools above, machining accuracy is guaranteed at the time of shipment, however, subsequent usage causes thermal displacement of the main shaft due to heat generated by a heat source such as a motor and a bearing. Thus, it is very important to correct the thermal displacement above in order to maintain machining accuracy.
With regard to the thermal displacement, especially a main shaft is sometimes largely displaced in a fore-and-aft direction thereof due to heat generated by a motor and a bearing. In that case, machining accuracy may decrease because errors occur in a machining amount in the fore-and-aft direction of the main shaft.
Japanese Patent Laid-Open JP2006-281335A discloses a technique as means for solving the problem above, in which temperature of respective components of a machine tool is measured, and thermal displacement is estimated on the basis of the measured temperature and a coordinate of a blade edge position.
Japanese Patent Laid-Open JP2006-116663A discloses a technique of calculating thermal displacement on the basis of a load and a rotation speed of a main shaft, and an amount of last thermal displacement.
Japanese Patent Laid-Open JP2013-82022A discloses a technique of determining a correction amount from a difference between a coordinate at the time of first contact detection and a coordinate at the time of second contact detection on the basis of detection of a detector in order to eliminate or reduce duration of a warm-up operation.
In the technique disclosed in Japanese Patent Laid-Open JP2006-281335A, since it is required to attach a sensor for temperature measurement to each of portions inside a machine tool to measure temperature of respective components of the machine tool, it is thought that possibility of failure in attached sensors may increase to cause a cost increase.
In the technique disclosed in Japanese Patent Laid-Open JP2006-116663A, since calculation is performed on the basis of a load and a rotation speed of the main shaft, it may be difficult to estimate the displacement in consideration of factors other than an operation of the machine, such as circumstances where the machine is installed.
In the technique disclosed in Japanese Patent Laid-Open JP2013-82022A, since a contact sensor is used for performing detection at the time of the contact detection, there is a possibility that appropriate detection cannot be achieved, or effort of maintenance of the sensor is required depending on the reliability of the sensor.